1. Field of the Invention
The present invention relates to a single-canister underwater stereocamera system with a distance measurement function capable of measuring the actual distance of a target underwater object from the system and, more particularly, to a single-canister underwater stereocamera system having two parallel cameras, two parallel lens units and a single motor, with the two parallel cameras and the two lens units being commonly operable by the single motor such that the two cameras are movable to the front and back and the two lens units are movable to the left and right, and so the stereocamera system effectively obtains a desired stereoscopic image of a target underwater object regardless of the distance of the target object from the camera system.
2. Description of the Prior Art
In recent years, techniques for controlling unmanned underwater vehicles (UUV) or remotely operated vehicles (ROV) performing a variety of underwater works have been quickly and highly developed. Therefore, it is possible for an operator in a surface vessel to direct an unmanned underwater vehicle (UUV) or a remotely operated vehicle (herein below, the UUV and ROV will be referred to simply as “ROV” for ease of description), submerged under water to perform a desired work in deep-sea, through a remote control process. In order to perform a deep-sea work using such an ROV, it is necessary to use underwater camera systems. In order to allow an operator to observe the area in front of an ROV and to actuate a robot arm of the ROV, most conventional ROVs are equipped with one monocular camera system. Of course, some ROVs provided with two or more monocular camera systems have been proposed and used. However, in the case of an ROV with such two or more monocular camera systems, the object of the installation of said camera systems is to observe two or more different sites covered by the camera systems. This means that each camera system is limited in its viewing angle. Such a conventional monocular camera system fails to provide a stereoscopic image, and so an operator on the surface vessel cannot measure or calculate the actual distance of a target underwater object from the camera system. Therefore, it is very difficult to perform a desired underwater work using such an ROV. In addition, the conventional monocular camera system undesirably causes an operator to finally feel fatigue in his eyes when he controls the ROV for a lengthy period of time while viewing the flat images displayed on a screen. Therefore, it is desired to provide an underwater stereocamera system capable of forming stereoscopic images.
In the prior art, such an underwater stereocamera system capable of forming a stereoscopic image of an underwater object has been typically accomplished by two cameras installed on a single camera platform. In such a case, the two cameras commonly track a target underwater object to form images of said object, and combine the images into a stereoscopic image of the object. However, such a typical stereocamera system is problematic in that it is necessary to precisely control the two cameras so as to allow them to commonly track the target object. It is also necessary to precisely control the focuses of the two cameras, and so the construction of the control unit for such typical stereocamera systems is undesirably complicated. Another problem of such a typical stereocamera system resides in that the system has to be precisely installed on a camera platform, thus requiring the platform to be precisely machined.
In recent years, an underwater stereocamera system capable of forming a stereoscopic image of an underwater object using two parallel cameras has been proposed and used. This stereocamera system is designed on the basis of the fact that there is a linear relation between the variation in the focus length of the two parallel cameras and the variation in the interlens distance of the cameras when the cameras simultaneously track a far-distant object.
However, this underwater stereocamera system is problematic in that it cannot form a desired clear stereoscopic image of a near-distant object since the expected linear relation between the variation in the focus length of the two parallel cameras and the variation in the interlens distance of the cameras is not maintained when the cameras simultaneously track such a near-distant object. In addition, the underwater stereocamera system with such two parallel cameras is designed such that both the variation in the focus length of the cameras and the variation in the interlens distance of the cameras are linearly controlled by adjusting the intercamera distance in place of adjusting the interlens distance of the cameras for ease of mechanical fabrication of the camera system. However, such a structure of the stereocamera system undesirably enlarges the dimensional error of stereoscopic images of near-distant objects.
As well known to those skilled in the art, the visual range under water is exceedingly limited. In addition, the underwater works, performed by the robot arms of ROVs, are typically limited to near-distant objects positioned within a reaching range of 1˜2 m. Therefore, it is practically necessary for underwater stereocamera systems to form clear stereoscopic images of near-distant target objects in place of far-distant objects. However, the conventional underwater stereocamera system with two parallel cameras cannot form desired clear stereoscopic images of near-distant objects even though it can obtain such desired clear stereoscopic images of far-distant objects. Therefore, it is necessary to provide an underwater stereocamera system capable of forming desired clear stereoscopic images of near-distant objects under water.
During an underwater work performed by an ROV, it is possible to improve the operational efficiency of an operator of the ROV by allowing the operator to measure or calculate the actual distance of a target object. A method of measuring the actual distance of a target underwater object using sonar has been proposed and used. However, the actual distance measurement performed by the conventional sonar is limited to large-sized objects, of which the actual sizes are larger than an effective critical size determined by the operational frequency of supersonic waves radiated from the sonar. Therefore, the conventional sonar cannot be used for measuring the actual distances of small-sized objects under water. Therefore, it is necessary to provide a means capable of visually measuring the actual distances of small-sized objects under water.